PEOPLING × GENETICS

Out of Africa

~70,000–50,000 years ago

Palaeolithic · Middle Stone Age · Last glacial

Between about 70,000 and 50,000 years ago, the Homo sapiens populations from which almost all non-Africans descend spread out of Africa.

The expansion out of Africa designates the dispersal of Homo sapiens populations from which almost all present-day non-African genomes descend, placed between about 70,000 and 50,000 years ago. These populations met Neanderthals in the course of their advance and mixed with them. The admixture occurred once, between 49,000 and 45,000 years ago, and left about two per cent of Neanderthal DNA in all their descendants. That shared proportion constitutes the argument: admixture occurring separately, after the groups had diverged, would have left different proportions and different segments in each population, so that their identity implies a single connected population at that date. The dispersal reaches all habitable continents within the following twenty millennia.

Why it matters

The episode is the node from which most non-African ancestry derives: European, Asian, Australian and Native American populations descend chiefly from the same expansion and carry its common marker, a comparable share of Neanderthal DNA. The remainder of the species' history stays African, the populations of the continent being by then some two hundred and fifty millennia old.

Dating & uncertainty

Earlier departures are documented by fossils, in the Levant around 180,000 years ago and again between 120,000 and 90,000. They left no notable trace in present-day genomes, which distinguishes them from the expansion proper. The interval retained, 70,000 to 50,000 years, dates the latter; genetic clocks constrain its later stages but not its starting point.

Our species’ history as one day

18:40:005 h 20 min before midnight

if the 315,000 years of Homo sapiens were compressed into a single day